The present invention relates to a driver circuit for a coil type tone generator that is effective to cause the tone generator to produce a pleasant sounding chime. The circuit is particularly that it is simple and inexpensive to manufacture, and is relatively immune to the effects of extraneous electrical devices.
In general, the circuit includes a high frequency oscillator and a low frequency oscillator. The high frequency oscillator established the tone of the chime and the low frequency oscillator provides the "striking" rate of the chime. The oscillators comprise simple logic gate circuits which are adapted to produce a decaying sawtooth type signal. The outputs from the two oscillators are combined so that the high frequency signal is superimposed onto the low frequency signal. The resulting signal is then pulse width modulated by providing the same through a logic gate. The modulated square wave signal is supplied to the base of a driver transistor which controls the excitation of the coil. The effect of modulating the signal is to cause the transistor to cycle on and off with the percent on-time of the transistor varying in accordance with the duty cycle of the waveform. Thus, as the duty cycle of the signal rapidly increases and gradually decreases, the tone generator produces a chime and decay, chime and decay.
Further objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :